A vacuolar Na+/H+ antiporter gene, IbNHX2, enhances salt and drought tolerance in transgenic sweetpotato

Abstract

Plant vacuolar Na+/H+ antiporters (NHX) play a critical role in adaption to abiotic stresses by compartmentalizing Na+ into vacuoles from the cytosol. In this study, a vacuolar Na+/H+ antiporter gene, named IbNHX2, was isolated and characterized from salt-tolerant sweetpotato (Ipomoea batatas (L.) Lam.) line ND98. IbNHX2 consisted of 542 amino acid residues with a conserved binding domain ‘FFIYLLPPI’ for amiloride and a cation/H+ exchanger domain, and shared a high amino acid identity (73.72–96.13%) with the identified vacuolar Na+/H+ antiporters in other plant species. The genomic DNA of IbNHX2 contained 14 exons and 13 introns. Expression of IbNHX2 was induced by abscisic acid (ABA), NaCl and polyethylene glycol (PEG). Its overexpression significantly enhanced salt and drought tolerance in the transgenic sweetpotato. An significant increase of proline content and superoxide dismutase (SOD) and photosynthesis activities and significant reduction of malonaldehyde (MDA) and H2O2 content were found in the transgenic sweetpotato plants. Up-regulation of the stress-responsive genes encoding pyrroline-5-carboxylate synthase (P5CS), SOD, catalase (CAT), zeaxanthinepoxidase (ZEP), 9-cis-epoxycarotenoid dioxygenase (NCED), aldehyde oxidase (AO), late embryogenesis abundant protein (LEA), psbA and phosphoribulokinase (PRK) in the transgenic plants was also found under salt and drought stresses. The overall results demonstrate the explicit role of IbNHX2 in conferring salt and drought tolerance of sweetpotato. The IbNHX2 gene has the potential to be used for improving salt and drought tolerance of plants.